"If you're working with huge files or a huge number of files, use XFS" went the slogan.

I was hit by this recently - with our 500ish (!!) entries in /node_modules and their dependencies of dependencies of dependencies, a standard 8GB VM formatted with ext4 just simply didn't have enough inodes for us to have two copies of our app (deployment swapover). Had to increase the size to 20GB, just to get the extra inodes. XFS would have handled it much better (from testing on a parallel machine). It was inode exhaustion, though the 'disk full' error message was the same - confusing at first, as df showed 40% free space...